The present invention relates to the art of coated papers and more particularly to a method and apparatus for the fabrication of a two-side coated manifold sheet in which at least one of the coatings is formulated with a pressure-sensitive material.
The present invention will be described with reference to the manufacture of a manifold sheet adapted for use as an intermediate sheet of a manifold assembly and in which the manifold sheet is sometimes referred to as a colorless carbon. It will be understood that the concepts of the present invention will have application also to the manufacture of other two-side coated paper products in which one or both of the coatings contain materials which are pressure-sensitive such as a coating containing pressure-rupturable capsules.
In U.S. Pat. Nos. 2,712,507, 2,730,456, 2,800,457, 3,996,405, and 4,001,140, reference is made to microcapsular or CB coatings wherein there is contained within the microcapsule a solution of a basic chromogenic material which is to be reacted with an acidic color-activating substance to produce a mark. Separate coatings are provided on suitable carrier sheets in which one of the coatings is formulated to contain a liquid reactant such as a colorless dye component dissolved in a liquid solvent and which is encapsulated in microscopic capsules uniformly distributed throughout the coating (hereinafter referred to as the emulsion coat), while the other coating is formulated of a reactive material, advantageously a phenolic polymer, which is adapted to react with a liquid when released from the capsule to form a colored image (hereinafter referred to as the reactive coat or the clay coat). U.S. Pat. Nos. 3,455,721, 3,672,935, and 3,732,120 are exemplary of the use of phenolic polymers as the reactive material. In addition, the reactive material can be a combination of a zinc compound and a salicylic acid derivative such as defined in U.S. Pat. No. 4,022,936. The reactive component can also be materials such as silton clay, silica gel, attapulgite and the like.
When the coating containing the encapsulated liquid is positioned in surface contact with the reactive coating, no color develops until pressure is applied by pen, pencil, stylus, typewriter key, die impression or the like, or by heat to rupture the capsules in the imaged areas whereby the liquid released from the ruptured capsule wets out the adjacent receptive material in the reactive coating to develop the image.
In addition to the above-named common types of CB coatings, there are also CB coatings where the acidic reactant is contained within the microcapsular coating as disclosd in U.S. Pat. No. 3,894,168. Also, there are color reactant systems which are not based on acid-base chemistry, as shown in U.S. Pat. No. 3,558,341.
In a manifold assembly, the top sheet in the assembly will be fabricated with only its underside coated with the emulsion coat, while the bottom sheet in the assembly will be coated on its top side with only the reactive coating. All of the sheets in between will be coated on the underside with the emulsion coat and on the top side with the reactive coat in a two-side coated sheet.
Since the emulsion coat comprises the most expensive materials and therefore represents the more expensive coating, it is desirable to fabricate the reactive coat with a high degree of surface smoothness so as to be able to make more effective contact with the emulsion coat and maximize the utilization of the encapsulated liquid released from the coating. In the light of the fact that the emulsion coat is sensitive to pressure which might rupture the capsule, it has been the practice to coat the paper first with the reactive coat whereby the latter can be calendered to smooth the coating before application of the emulsion coat.
Prior to the present invention, carbonless paper known as CFB which comprises a sheet of paper with a capsular coating on the back side and a reactive coating on the front side was produced either by applying a single coating to each side in two separate passes through a single side coater or by applying a coating to each side with two coating heads in a subsequent manner on a tandem coater. U.S. Pat. Nos. 3,535,140 and 3,632,378 are exemplary of methods for the manufacture of a dual-coated manifold sheet in tandem in a single coating pass. U.S. Pat. No. 3,535,140 discloses a method of coating a CFB sheet in a continuous operation by first coating one side of a web of paper with a microcapsule slurry by means of an air-knife station, drying the microcapsular slurry coating, coating the opposite side with a clay slurry by means of an air-knife station, and then drying the clay coating. In U.S. Pat. No. 3,632,378, a CFB sheet is coated in a continuous operation by first coating one side of a web of paper with a clay slurry, drying the clay coating, calendering the clay-coated sheet, coating the opposite side with a microcapsule slurry and drying the microcapsular coating. CFB production by either of the above methods results in significant curl and dimensional instability of the coated paper. Although correction apparatus installed prior to the reel is used to reduce these quality defects, the printer continues to have problems with curl and dimensional instability. In addition, the use of two coating heads, two discrete dryers, and correction apparatus necessitates a machine which requires much space and a high capital investment.
According to a known method, described in U.S. Pat. No. 3,489,592, a satisfactory coating result was obtained by guiding the web of material, for example paper, in a substantially vertical direction downwardly through a press nip which is formed between a thin, flexible blade in the form of, for example, a steel blade with a sharp edge and a rotating roller, the space between the blade and the roller forming a dam filled with a coating composition. Immediately after passing through said nip, the paper web is deflected toward the side where the blade is located, so that an angle is formed between the tangent of the roller and the downward passing portion of the web thereby avoiding a film splitting. However, this known method which utilizes the Billblade coater, only permits the use of the same coating compositions on both sides of the paper web. The reasons for this is that the same dam or coating puddle surrounds the paper web and it has been found to be extremely difficult to arrange a suitable device to separate the dam, for example, into two dams, one for each side of the web, so as to permit a coating with different coating compositions on each side of the paper web.
The invention as defined in U.S. Pat. No. 3,489,592, that is, the original Billblade invention, was then modified to allow the application of different coatings to both sides of a sheet, as shown in U.S. Pat. No. 3,899,615. In this patent, a roll with a soft rubber covering forms a pressure nip with a chrome-finished roll such that coating from a puddle is metered onto the surface of the chromed roll. This coating is then transferred to a paper web at the same time that a different coating is metered to the opposite side of the paper web by a blade. The generally used coating compositions with this method and apparatus are a starch solution metered from the puddle formed between the pressure nips of the soft rubber roll and the chrome roll and a clay coating formed as a puddle between the blade and the rubber-covered backing roll.
Although a reactive coating can be applied successfully on the blade side of the above system, the roll side is unsuitable for the application of capsular coatings. This is true for three reasons:
(a) The pressure nip formed between the rolls does not allow enough coating to be transferred to the web;
(b) A poor pattern occurs on the web because of film splitting at the nips formed by the rolls; and
(c) The capsules are damaged by the pressure nips.
British Pat. No. 1,361,996 discloses a process for making CFB paper and printing an ink image, all in one pass in a single machine. The methods of application of both the microcapsular and reactive slurries are both film-coating stations wherein the films are applied in sequence with an intermediate drying after each application. The apparatus in the British Patent has etched or anilox rolls in each of the application stations.
Capsular coatings have been successfully applied to a paper web with a flexographic press which utilizes an anilox roll. An anilox roll is a chrome-covered roll which has precisely machined cells below its surface which will carry a volume of coating after extra material is completely removed from the roll's surface. With the use of an anilox roll, a uniform, well-regulated amount of coating can be applied to a paper web with no damage to the capsules. However, nowhere in the prior art can there be found any method or apparatus wherein a manifold sheet having a relatively smooth, curl-free coating of a reactive composition on one side and a relatively smooth, curl-free coating of rupturable encapsulated material on the opposite side can be produced by simultaneously coating both sides of the manifold sheet in a single coating pass without the application of pressure for smoothing either of the coatings.
Accordingly, it is an object of the present invention to provide a method and apparatus for producing a two-side coated paper of the type described wherein the coatings are sufficiently smooth and uniform throughout the surface of the sheet and wherein the coated sheet is relatively free of curl and dimensional instability so as to lie flat in the manifold assembly.
Another object of the present invention is to provide a method and apparatus for simultaneously coating both sides of a manifold sheet wherein the use of one of the coating heads, one of the discrete dryers and the correctional apparatus can be substantially eliminated, thereby substantially reducing the space requirements and high capital investment.
A further object of the present invention is to provide an improved method and apparatus for simultaneously coating both sides of a manifold sheet wherein one of the coatings is a rupturable encapsulated material which can be applied to one of the sides of said manifold sheet without danger of rupturing said capsular coating.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Pursuant to the present invention, the above-identified deficiencies can be eliminated and an effective method and apparatus for simultaneously coating a manifold sheet with a capsular coating on one side and a reactive coating on the other side thereof can be achieved by combining the technology of the flexographic press and the Billblade coater. Thus, a coating containing capsules is puddled into a nip formed by a rubber-covered metering roll and an anilox roll. The rubber roll runs at a much slower speed than the anilox roll in order to remove any coating from the surface of the anilox roll which is not contained in the cells of the anilox roll. Preferably, a doctor blade operatively associated with the surface of the anilox roll can also be used for this purpose. A rubber-covered backing roll is then provided for removing the coating from the cells at the nip that it forms with the anilox roll and the capsular coating is then subsequently transferred to the back of a paper web at the same time that a reactive coating is metered onto the other side of the paper web by a backing blade. This results in a uniform application of coatings to both sides of the web with no capsule damage. By proper selection of the cell size in the anilox roll, sufficient CB coating can be applied to produce a satisfactory carbonless paper which has no curl or dimensional instability.
The present invention is also effective when starch is applied with the anilox roll and a reactive coating is applied with a backing blade since it allows much greater latitude in the amount of starch applied such that no curl exists on the CF paper. In addition, the CB coating can be applied on the anilox roll side of the web and starch can be applied on the blade side of the web, and again, the starch application can be controlled such that no curl exists in the paper after drying.